@article{PIM_1971_N_S_11_25_a7,
     author = {Petar M. Vasi\'c and Jovan D. Ke\v{c}ki\'c},
     title = {A {Generalisation} {Of} {The} {Concept} {Of} {Convexity}},
     journal = {Publications de l'Institut Math\'ematique},
     pages = {53 },
     publisher = {mathdoc},
     volume = {_N_S_11},
     number = {25},
     year = {1971},
     url = {http://geodesic.mathdoc.fr/item/PIM_1971_N_S_11_25_a7/}
}